Tire pressure indicator

Abstract

A wheel-mounted tire pressure indicator which includes a housing enclosing a pneumatically-actuated pressure indicia scale as well as a self-contained battery and circuit for energizing a signal light on the housing when the tire pressure is below a predetermined selected value.

We claim: 
     
       1. A tire pressure indicator comprising a housing having means thereon for attaching it to a vehicle wheel, a cylinder in said housing, a piston slideable axially in said cylinder, a switch actuator supported by said piston for movement therewith, means on said cylinder adapted to be connected with the valve stem of a vehicle tire for subjecting one side of the piston to the pressure of the air in the tire, a spring yieldably opposing movement of the piston in response to the air pressure exerted against said one side thereof so that the position of said switch actuator in a direction axially of said cylinder is determined by the extent to which the tire air pressure overcomes the force on the piston produced by said spring, an indicator light on said housing and means in said housing forming an electrical circuit for energizing the indicator light, said circuit means including a switch disposed in said housing in a predetermined position axially of said cylinder for actuation by said switch actuator when the tire pressure is below a predetermined value and thereby energize said signal light. 
     
     
       2. A tire pressure indicator as called for in claim 1 wherein said housing has a viewing aperture therein and including a visual indicator fixed to and movable with said piston, said visual indicator having indicia thereon visible through said viewing aperture for visually indicating the tire pressure relative to said predetermined value. 
     
     
       3. A tire pressure indicator as called for in claim 2 wherein said viewing aperture is closed by a transparent window having indicia thereon, said indicator being fixed to said piston and said switch being positioned relative to said switch actuator such that the signal light is energized only when the position of the indicia on the indicator is displaced relative to the indicia on said window to indicate that the tire pressure is below said predetermined value. 
     
     
       4. A tire pressure indicator as called for in claim 3 wherein the indicia on said indicator comprises a plurality of differently colored bands spaced axially along said indicator. 
     
     
       5. A tire pressure indicator as called for in claim 4 including a manual switch on said housing in parallel circuit with said first-mentioned switch, said manual switch being actuatable to close said circuit to said signal light to determine whether or not the circuit and signal light are in operating condition. 
     
     
       6. A tire pressure indicator as called for in claim 1 wherein said circuit means is mounted on a circuit board, said housing having means therein for locating said circuit board in a fixed predetermined position therein, and means for adjusting said switch on said circuit board in a direction axially of the cylinder. 
     
     
       7. A tire pressure indicator as called for in claim 1 wherein said switch actuator comprises a magnet and the switch closes when the magnet moves in one direction to a predetermined position in close proximity to said switch. 
     
     
       8. A tire pressure indicator as called for in claim 7 wherein said switch comprises a reed switch. 
     
     
       9. A tire pressure indicator as called for in claim 8 including means for adjusting the position of said reed switch in a direction parallel to the axis of the cylinder to vary the position at which the magnet closes said switch. 
     
     
       10. A tire pressure indicator as called for in claim 8 wherein said piston projects axially beyond said cylinder at one end thereof and including an annular member secured to said end of said piston, said magnet being seated in said annular member and being retained therein by said spring. 
     
     
       11. A tire pressure indicator as called for in claim 10 wherein said annular member has an outer surface provided with axially spaced indicia thereon for designating the tire pressure relative to said predetermined value, said housing having a viewing aperture therein registering with said indicia. 
     
     
       12. A tire pressure indicator as called for in claim 11 wherein said indicia is divided into a plurality of axially successive zones, one of said zones designating said predetermined pressure and being spaced intermediate the other zones, said other zones designating the extent to which the tire is over- or under-inflated. 
     
     
       13. A tire pressure indicator as called for in claim 1 wherein said cylinder has a large bore and a concentric smaller bore, said piston comprising a rod slideably arranged in the smaller bore with a close fit and having a head at one end slideably arranged in said larger bore. 
     
     
       14. A tire pressure indicator as called for in claim 13 wherein said rod is formed of a non-magnetic metal and said smaller bore is formed of a low-friction plastic material. 
     
     
       15. A tire pressure indicator comprising a non-magnetic housing adapted to be mounted on a vehicle wheel, a non-magnetic cylinder in said housing projecting outwardly of the housing at one end for connection with a conduit extending from the valve stem of the vehicle wheel tire so that the tire pressure is applied to the cylinder, said cylinder having a non-magnetic piston slideably arranged therein, said piston being biased axially away from said one end of the cylinder in response to the application of air pressure from the tire at said one end thereof, said piston having one end projecting axially outwardly beyond the other end of the cylinder, a non-magnetic retainer fixedly mounted on said projecting end of the cylinder, a magnet mounted on said retainer, a compression spring bearing against said retainer at one end with its opposite end bearing against a wall of said housing for biasing said piston toward said one end of the cylinder, a signal light on said housing and means in said housing forming a circuit for energizing said light, said circuit means including a magnetically responsive switch for closing the circuit to the light when the magnet is displaced axially of the cylinder to a position in close proximity to said switch. 
     
     
       16. A tire pressure indicator as called for in claim 15 wherein said piston comprises a metal rod extending axially of the cylinder, said cylinder having at least two stepped concentric bores through which the rod extends, one of said bores being defined by a bushing formed of a low-friction plastic material having a close sliding fit with said rod and an O-ring in the other bore sealingly engaging said rod. 
     
     
       17. A tire pressure indicator as called for in claim 16 wherein the end of the cylinder through which said rod extends has an outer surface spaced radially from the walls of said housing, said retainer comprising an annular sleeve having a radial partition intermediate its ends, said rod being secured to said partition, one end portion of said sleeve overlying said outer surface of the cylinder, said magnet being seated in the other end portion of said sleeve. 
     
     
       18. A tire pressure indicator as called for in claim 17 wherein said sleeve has a cylindrical outer surface with axially spaced indicia thereon, said indicia extending axially along both portions of said sleeve and a viewing aperture in said housing through which only a portion of said indicia is visible, the indicia visible through said aperture being indicative of the extent of inflation of the tire. 
     
     
       19. A tire pressure indicator as called for in claim 18 including a valve stem connected to said cylinder and in communication with one end thereof, said valve stem extending through said housing to the exterior thereof and being adapted for connection to a source of air under pressure for directing air to the valve stem on the tire through said cylinder. 
     
     
       20. A tire pressure indicator as called for in claim 18 including means in said housing for limiting the extent of axial displacement of the piston in the direction opposed by said compression spring.